The present invention relates generally to fluid seals, and more particularly, to radial shaft seals with an elastomeric portion and a resinous ring portion.
Shaft seals incorporating resinous sealing rings are known in the prior art. Examples of these are found in U.S. Pat. Nos. 5,791,658 and 5,921,555 which are owned by the assignee of the current application. Resinous sealing rings made of polymers such as polytetrafluoroethylene (PTFE), or the like, are characterized by a very lubricious surface that has several advantages. For example, they resist rapid wear, are relatively chemically inert and perform well in relatively dry environments, such as those where all or part of the seal is not immersed in oil.
However, a resinous sealing material has its limitations. As the resinous sealing material becomes less flexible, it loses its ability to follow the shape of the shaft surface which it sealing and it is also subject to cold flow or creep.
On the other hand, elastomeric materials have been used for sealing applications for nearly seventy years. Elastomeric seals are used in sealing applications because they are relatively rugged, resilient, can be designed for a snug fit over an associated shaft and they retain elasticity over a long period of time. However, elastomeric seals also have limitations, such as limited chemical resistance, and they do not perform well in relatively dry environments.
Thus, there is a need to combine elastomeric materials and resinous materials into one composite shaft seal that optimizes the attributes of each material while reducing the disadvantages of these materials. One example of his is U.S. Pat. No. 4,986,553 where a thin layer of elastomeric material covers and is bonded to the surface of a flexible PTFE ring component. In use, the PTFE ring component presses down on a substantial width of the elastomeric sealing surface until the sealing surface wears away with time against the radial shaft. Thus, the PTFE ring component and the layer of elastomeric material both contact the radial shaft in order to prevent the migration of fluid past the sealing band of the composite seal. However, it has been found that the wear performance of this seal is not satisfactory. This is because the major portion of the initial contact load on the seal is carried by the elastomeric sealing surface, there is a tendency for the elastomeric portion to shred into pieces and these shredded pieces may wedge into and damage the seal contact surface with the radial shaft surface.
Thus, none of the known prior art designs utilizes a composite seal against the radial shaft in which the elastomeric section provides the major static and dynamic sealing functions and in which the resinous portion carries a major portion of the contact load so that after initial wear in, the contact load at the edge of the composite seal is carried by the resinous portion and the sealing function is accomplished by the elastomeric section.
The present invention seeks to provide a solution to the above problems and provide a composite shaft seal in which the elastomeric section at its distal end provides a static seal and the pumping action for dynamic sealing against the radial shaft and in which the distal end of the resinous portion provides chemical and wear resistance and low friction and carries a majority of the contact load support for the sealing lip. In pressurized applications, the resinous portion provides stiffness to the elastomeric section to limit distortion of the elastomeric section and to prevent a substantial increase in contact load on the sealing lip due to pressure acting on the resinous portion of the elastomeric member with the shaft.
The present invention discloses a composite shaft seal adapted for sealing against a dynamic shaft. The shaft seal includes a case member and a resilient sealing body attached to the case member. The sealing body has an annular elastomeric member and a resinous ring. The elastomeric member has a radially extending section and a distal end portion. The resinous ring has a radially extending portion and a radial contact edge. The radially extending section is contiguous to the radially extending portion having a sealing edge. The sealing edge is biased to form an interference fit with the distal end portion of the shaft for dynamic and static sealing and the radial contact edge supports a major portion of the radial reaction forces of the resinous ring so as to engage the shaft in fluid tight relation and to reduce wear on the distal end portion.
It is an object of the present invention to provide a composite seal in which the distal edge of the elastomeric member provides both static sealing and dynamic sealing against the shaft and in which the edge of the resinous portion provides chemical and wear resistance and low friction and absorbs a major portion of the contact support load for the distal edge of the elastomeric member.
It is another object of the present invention to provide a composite shaft seal for pressurized applications in which the resinous ring provides stiffness to the elastomeric member to prevent distortion to the elastomeric member and to reduce the amount of contact load the elastomeric member must absorb when contacting the shaft.